The present invention relates to the production of steel from raw materials, and particularly to a method and apparatus for continuous electric arc furnace steelmaking and foundries having minimal emissions and electrical energy demand while maximizing steel or iron production in mini-mills and foundries. The invention is ideally suited for providing energy conservation and environmental protection while maximizing production.
The existing CONSTEEL Process and Apparatus, as described in U.S. Pat. No. 6,155,333 to Vallomy, requires two conveyors, a connecting car and ample space to achieve the above objectives and is most suitable for foundries having a high feed capacity. However, the CONSTEEL apparatus is may be cost prohibitive for smaller foundries and mini-mills in the feed capacity range of 23-35 tons per hour. Furthermore, smaller foundries and mini-mills may not have sufficient space to accommodate the CONSTEEL apparatus.
The production of steel and steel products, or products that incorporate steel therein, are essential to the maintenance and growth of many economies in various parts of the world. The acquisition and installation of steel refining facilities depend on a number of important considerations including environmental impact, cost efficiency and available space. The manufacture of steel using an electric arc furnace (EAF) is a highly advantageous process in the modem steel industry because of the flexibility of the EAF in using mixes of different charge materials including liquid hot metals and the ability to produce substantially all known grades of steel.
One approach to refining steel is the use of continuous EAF charging, melting and refining systems having side feeding of the EAF, such as described in U.S. Pat. No. 6,155,333 (""333) (the CONSTEEL apparatus and method), U.S. Pat. No. 4,543,124 (""124) and U.S. Pat. No. 5,800,591 (""591). The systems described in the ""333, ""124 and ""591 patents provide continuity to the preheating of charge materials, the melting of charge materials, and the refinement of steel. Such continuous preheating, melting and refining systems incorporate furnaces having a furnace design that accommodate side feeding and off gas extraction at low gas flow velocities so that particulate entrained in the off gas falls out in the preheater. In these systems, a charging pan is located about a material entry opening in the side of the furnace. Charge material is introduced from the pan into the furnace, and CO rich off gas is transferred to the charge preheater to be used as a fuel for preheating purposes. The systems described in the ""333, ""124 and ""591 patents are energy conservative.
However, mini-mills and foundries have a limited space and limited production which make the CONSTEEL Continuous Preheating System or a mere overall reduction in length thereof, cost prohibited and consequently an unsuitable method and apparatus. What is needed is an improved method and apparatus for preheating, melting, and refining steel that is compatible with limited capacity facilities. Further needed is a method and apparatus for preheating, melting, and refining steel that permits side feeding into a furnace without requiring an increase in the furnace height and maintains the consistency of charge feeding.
Continuous steel preheating, melting and refining systems that have side feeding use equipment that interface with the furnace, such as a connecting car, is described in U.S. Pat. Nos. 4,681,537, 4,836,732 and ""591. Such equipment is prone to damage by heat and abrasion and require periodic maintenance. For example, the connecting car pan is exposed to the splash of molten steel and slag and to high temperature peaks of off gas. Consequently, the refining process may be interrupted by downtime required for the repair and maintenance of the connecting car.
What is needed is a method and apparatus for preheating, melting and refining steel in mini-mills and foundries that is cost effective at limited production rates and which facilitates repair and maintenance of charge feeding equipment that interface with the furnace.
The present invention is an improved method and apparatus for continuous electric steelmaking. The invention permits side feeding into a furnace without requiring an increase in the furnace height and allows repair and maintenance of connecting means that directly feeds charge materials to the furnace with less downtime. Additionally, the present invention also simply and quickly allows the connecting means to be interchangably positioned within a furnace opening in a charging position, partially positioned in the furnace opening in a retracted position for top charging the production of alloyed speciality steel, and fully withdrawn from the opening for quick repair and maintenance of the apparatus.
The invented apparatus for continuous preheating of an iron-bearing material, and melting and refining of steel in a metal-producing furnace comprises an elongate conveyor having a front, intermediate and rear section. The conveyor is mounted on a frame having wheels for longitudinal movement toward and from the furnace. A loading section is disposed at the front segment for receiving charge materials. A covered and thus generally closed preheater for preheating the charge materials on the conveyor is disposed at the intermediate segment. A connecting means is disposed at the rear section of the conveyor, longitudinally moveable with the conveyor, and configured to longitudinally and removably insert into the furnace opening.
Additionally, the invented apparatus for continuous preheating of an iron-bearing material, and melting and refining of steel in a metal-producing furnace comprises a conveyor for receiving charge materials, a covered and thus closed preheater for preheating the charge materials on the conveyor, a metal treating furnace for melting and refining a metallic charge. a connecting means removably coupled to the preheater and to the charge conveyor for directly feeding charge materials into a furnace bath, the connecting means being a round tubular member having a horizontal centerline, the furnace being tiltable about an axis of rotation coinciding substantially with the centerline of the connecting means, and the conveyor being mounted on wheels for longitudinal movement toward and from said furnace.
The connecting means comprises a quickly retractable connector having a substantially semi-circular or semi-round charging pan situated therein. The furnace comprises a shell that may be either a single or split shell structure, a furnace roof having vertical openings for receiving electrodes and the round charging opening. The charging opening has a top half positioned in the roof and a bottom half in an upper shell portion thereby accommodating a low furnace height.
The connector forms the terminal end of the conveyor adjacent to the preheater and is retractable with the conveyor along rails on which the feeding system is mounted. The retractable connector and split entry furnace opening facilitate and simplify the repair and maintenance of the connector to minimize steel producing downtime.
The invented method and apparatus improves mini-mill steel refining systems as well as foundry production.
A principal object of the present invention is to provide an improved apparatus for preheating, melting, and refining steel that conserves energy and protects the environment.
Another, more particular object the present invention is to provide a charging apparatus comprising a loading section, a preheater, a connecting means for engaging an opening of a furnace, and a conveyor extending the length of the charging apparatus for advancing charge materials to the furnace.
Another object of the present invention is for the conveyor to be mounted on wheels which moveably engage rails for longitudinally moving the charging apparatus away from and towards the furnace to a charging, retracted or disconnected positions.
Another object of the present invention is for the connecting means to be substantially round with a horizontal centerline, and for the connecting means to longitudinally and removably be insertable into furnace opening.
Another object of the present invention is for the conveyor to be supported by a frame, the loading section to be provided with a skirt and the preheater provided with a hood; and for the skirt and hood to be removably attached to the frame so that the skirt and hood longitudinally move with the charging apparatus away from and towards the furnace to the charging, retracted or disconnected positions.
Another object of the present invention is to further include a dynamic gas seal positioned between the loading section and the preheater.
Another object of the present invention is to include a burner in the preheater to supplement the preheating capability of the furnace off gas, if needed.